Two exonic genetic variants in apolipoprotein L1 (APOL1), common in those of recent African ancestry, have a major negative impact on the kidney health of African-Americans. While its association with kidney disease has been reproducibly demonstrated, the full genetic architecture of APOL1 associated nephropathy, and its underlying biology, is unclear. Without such knowledge, the ability to develop targeted pharmacologic therapies is remote. The long-term goal is to improve clinical outcomes for individuals who have APOL1- associated nephropathy. The overall objective here is to gain a deep understanding of the biology of APOL1- associated proteinuric disease by integrating genetic, intrarenal transcriptomic, morphologic, and clinical datasets derived from 720 human subjects with proteinuric disease enrolled in the Nephrotic Syndrome Study Network. The central hypothesis is that the high-risk APOL1 genotype, as well as increased APOL1 expression, results in APOL1-specific and genome-wide alterations of intrarenal gene expression, specific morphologic changes in the kidney, and worse clinical outcomes. The rationale for this proposal is that a more complete understanding of the genome biology of APOL1, as well as the intrarenal consequences of its aberrant forms, can lead to development of molecularly-based pharmacologic strategies to prevent/treat APOL1-associated proteinuric disease. The specific aims of the study will be to (1) Discover genetic factors at the APOL1 locus associated with its glomerular and tubulointerstitial mRNA expression, (2) Determine the clinical outcomes and biologic context associated with intrarenal mRNA expression of APOL1, and (3) Define morphologic signatures associated with APOL1-associated proteinuric disease. Aim 1 will pair genotyping data with renal biopsy-based, RNA-Seq-generated gene expression profiles on the gene and transcript level of specificity. Aim 2 will apply longitudinal model building and differential- and intercorrelated-gene expression methods to clinical and genome-wide transcriptomic data, respectively. Aim 3 will use deep quantitative and qualitative morphologic measurements of the glomerular, tubulointerstitial, and vascular compartments of over 650 biopsies. The contribution here is expected to be an increased understanding of the genetic architecture and potential biological mechanisms underlying APOL1-associated nephropathy, from a human-based, intrarenal perspective. This contribution will be significant because it will produce insights about APOL1- associated nephropathy with potential for direct translation into molecularly-derived, targeted therapeutic strategies. The research proposed in this application is innovative, in our opinion, because the discoveries made regarding the epidemiology and biology of APOL1-associated proteinuric disease will be directly derived not only from a large cohort of affected human subjects, but from the kidney tissue directly impacted by these genetic variants. Given the high-risk genotype's generalized negative impact across kidney conditions, discoveries made here may be extended to improve the health of a larger group of African-Americans beyond those with proteinuric disease.